Method and apparatus for catalytic conversion



Nov. 15,- 1949 J. M. PAGE, JR

METHOD AND APPARATUS FOR CATALYTIC CONVERSION Filed Jan. 31, 1941 2Sheets-Sheet 1 N Q R fiuenzar."

QQQRQNNUWUDN Q/amzes/iPgg/ri M 11 0. M j dzfor/v ey Nov. 15, 1949 J. M.PAGE, JR

METHOD AND APPARATUS FOR CATALYTIC CONVERSION Filed Jan. 31, 1.941

2 Sheets-Sheet 2 V nifias A. l- 6/ -27 .58 2/ 26 III A 28 I 89 50/ 2STRIP/ EB ll zerlas .PZ'HCTO Z4 16 52 fiacll'alzai orr .PZ'GZWEMTOB Air/j5 14. I Ij nerZGaS I'UENHCE 1 afar 15g Patented Nov. 15, 1949 DIETHODAND APPARATUS FOR CATALYTIC CONVERSION James M. Page, In, Chicago, 111.,assignor to Standard Oil Company, Chicago, 111., a corporation ofIndiana Application January 31, 1941, Serial No. 376,763 12 Claims. (C1.196-52) 'This invention relates to a catalytic conversion system and itpertains more particularly to a system for the catalytic production ofhigh quality motor fuel. Related applications in clude Scheineman Ser.No. 392,848, filed May 10, 1941; Scheineman Ser. No. 400,956, filed July3, 1941; Scheineman Ser. No. 440,566, filed April 2'7, 1942; GunnessSer. No. 400,958, filed July 3, 1941; and Johnson Ser. Nos. 392,846-7,both filed May 10, 1941.

In catalytic hydrocarbon conversion processes the endothermic reactionand exothermic regeneration can be effected while the catalyst issuspended in reacting vapors and regeneration gases respectively. Insuch systems the required pressure differentials are obtained by meansof a fluid head of dense aerated catalyst in a standpipe which in thissystem is called a catastat. My invention relates particularly to animproved method and means for combining the reactor, regenerator, andstandpipe.

An object of my invention is to avoid or minimize cooling of catalystafter regeneration. A further object is to provide a catalyst systemrequiring only one pressuring standpipe to obtain circulation of thepowdered or granular catalyst. A still further object is to control theregeneration and reaction temperatures.

Other objects will become apparent from the following detaileddescription read in conjunction with the accompanying drawings whichform a part of this specification and which schemat'ically representflow diagrams of my improved system as applied to a catalytic crackingsystem.

The above and other objects are attained by providing a regenerationzone above, and integral with, the standpipe and by heat exchangebetween the regeneration zone and reaction zone.

I claim no novelty in any catalyst per se and the selection of thecatalyst will depend upon the nature of the conversion process. Thecatalyst is preferably in the form of hard, porous particles of about150 to 400 mesh. The apparent density of the catalyst at rest can beabout 30 to 50 pounds per cubic foot. The catalyst is rendered fluent byaeration or by the use of upfiowing gas or vapor streams to a density ofbetween about to 25 pounds per cubic foot, for example about 20 poundsper cubic foot. With catalyst particles of 150 to 400 mesh size, Iprefer aeration at a superficial gas velocity of between about 0.1 and0.2 feet per second. It should be understood, however, that the linearvelocity of the aeration gas will be somewhat dependent 2 upon thecatalyst particle size, catalyst density, etc. Generally speaking thesuperficial velocity .of the aerating gas should be between about 0.05and 0.3 feet per second.

My invention can be applied to various conversion processes includingcracking, hydrogenation, dehydrogenation, aromatization, alkylation,isoforming, reforming, etc. but will be described with particularreference to catalytic cracking of heavy hydrocarbon oils to producehigh quality motor fuel.

Heavy hydrocarbons such as gas oil and vaporizable hydrocarbon oils ingeneral can be converted into gasoline with yields of between about 30and percent per pass by vaporizing the oils and contacting the vaporswith finely divided solid catalytic materials in suspension attemperatures within the conversion range, usually of the order ofbetween 800 F. and 1000 F.

Various catalysts can be used. It is preferred,

however, to employ solid cracking catalysts of the metal oxide type suchas silica-alumina, silica-magnesia, alumina-zirconia,silica-zirconiaalumina, silica gel promoted with metal oxides adsorbedthereon, for example magnesia and/or alumina, acid treated bentonite andother acid treated clays, for example Super Filtrol, and other naturaland synthetic catalystsof the solid metal oxide type.

A pressure of between about 0 and 50 pounds per square inch gauge, forexample 25 pounds per square inch, and a holding time, i. e., theaverage residence time of the catalyst within the reactor, of betweenabout 0.5 and 60 minutes, for example about 5 minutes, can be used. Aspace velocity,

i. e., volume of liquid oil per volume of catalyst in the reactor perhour, of between about 0.5 and 20, for example a space velocity of about5 can beused. The volume of catalyst is the volume occupied by thecatalyst present in the reactor at any one instant measured at rest. Itis contemplated that hi h space velocities will be used with low holdingtimes, and vice versa, these and other conditions being combined toeffect the desired degree of cracking. If desired the catalytic crackingcan be conducted in the presence of hydrogen. The use of smallamounts-of hydrogen cuts down the formation of coke very markedly andincreases the efilciency of the catalyst by decreasing the necessity ofregeneration.

My invention can be used in catalytic reforming of straight-run orcracked naphtha. Preferred catalysts in my process when applied toreforming are the oxides of the metals of the left-hand column of groupVI of the periodic table, particularly chromium, molybdenum andtungsten, but I can also use other metal oxides and other metalcompounds, particularly oxides of the metals of the left-hand columns ofgroups IV and V of the periodic table such as titanium, cerium, thoriumand vanadium. Moreover, while these catalytic oxides can be used aloneor on various supports including magnesia, I find it preferable toutilize them on alumina as a support. It will also be apparent thatmixed catalyst can be used.

When cracked naphthas are reformed I prefer I to use a pressure ofbetween about 30 and 250 pounds per square inch, for example between 30and 100 pounds per square inch. Straight-run naphthascan be treatedunder higher pressures of between 30 pounds per square inch and 450pounds per square inch, for example from 50 to 300 pounds per squareinch. An average catalyst bed temperature of at least 875 F. and nothigher than about 1075 F., for example a temperature of about 980 F. canbe used.

A space velocity, i, e., volume of liquid oil per volume of catalyst perhour, of between 0.04 and 10, preferably about 0.1 and 5.0, for examplea space velocity of about 1.0 can be used, the volume of catalyst beingthe volume of the catalyst present in the reactor at any one instantmeasused at rest or in the compacted condition. Catalyst holding timesmay vary over quite a wide range from less than one minute to more thantwenty-four hours.

The reforming is conducted in the presence of added hydrogen. I measurethe amount of hydrogen by the number of mols of hydrogen per mol ofcharge, calculated on the basis of the mean molecular weight of thecharge. A mol ratio of between 0.5 and 8 is preferred.

My invention is illustrated by the drawings in which like elements aredesignated by like reference numerals. Referring to Figures 1 and 2,

. the feed stock is introduced through line III by pump H to furnace l2wherein the charge is vaporized and heated. As the heated vapor passesthrough transfer line l3 it picks up powdered catalyst from standpipe orcatastat" M. The catalyst is introduced into the transfer line l3 inamounts regulated by slide valve or star feeder l5. It should beunderstood, of course, that steam or any other suitable means can beused for introducing the catalyst into transfer line I 3 and that thecatalyst is carried by the vapors in this line to upflow reactor I6. Ifdesired, the catalyst can be injected directly into the reactor ISinstead of being introduced into the transfer line l3.

Reactor [6 can be a cylindrical vessel with a conical inlet and outletrespectively and of such size and cross-sectional area as to retain thenecessary amount of catalyst for effecting the desired amount ofconversion. The cross-sectional area should be such as to insure avertical vapor velocity of between about 0.3 and 3 feet per second inthe reactor if the reaction is to be effected under the desired fluidphase conditions. For example a reactor having an inside diameter ofabout 13 feet and a height of about 33 feet and a vapor velocity ofabout 1.2 feet per second to give a catalyst density of about 11 poundsper cubic foot of reactor space is satisfactory. It should beunderstood, however, that my invention is not limited to any particularreactor size and shape and that it is only necessary to provide acontact of the vapors with a sufiicient amount of catalyst to effect thedesired conversion. Ve-

4 locities necessary to give a certain catalyst concentration willdepend on catalyst size.

The reactor |8 can be provided with suitable means in heat transferrelation with the regenerator l1. For example internal coils l8 and I!or an external shell can be used through which can pass mercury,diphenyl, or molten salts, for example. The heat transfer medium picksup heat in the regenerator l1 and transfers the heat to reactor l6. Thuswhen fresh feed to the process is heat exchanged, it is brought to theapproximate reaction temperature prevailing in reactor IB. If desiredthe reactor ll can be placed within the regenerator "as illustrated inFigure 2 of the drawings.

Reaction vapors carry catalyst from the top of the reactor It at thesame rate at which catalyst is introduced into the reactor after acertain quantity of catalyst has accumulated in the reactor andequilibrium is reached in the upflow reactor. This catalyst-vapor streamis introduced by line 20 into cyclone separator 2| from the base ofwhich spent catalyst falls through conduit 22 into stripper 23. An inertstripping gas such as steam is introduced through line 24 at the base ofthe stripping column 23. Reaction vapors leave cyclone separator 2|through line]! and these vapors, together with stripping gases from line26, are introduced into cyclone separator 21 from which the remainingcatalyst particles are returned to the stripper through conduit 28. Thevapors from separator 21 are conveyed by line 29 to a fractionationsystem for separating a gasoline fraction from lighter and heavierreaction products. It should be understood that any other catalyst-vaporseparation can be used instead of, or in conjunction with, the cycloneseparators and that any number of cyclone separators can be used eitherin series or in parallel for effecting the separation.

The reaction vapors pass by line 29 to fractionator 30. Gasoline andgases are taken overhead through line 3| and cooler 32 to reflux drum33. Gas can be vented from this receiver through line 38. A portion ofthe liquids can be recycled by valved line 35 and pump 36 as reflux intower 30. The balance of the liquid is conducted by valved line 31 tostabilizer 38. Gas oil from fractionator 30 is withdrawn by valved line39 and all or a portion recycled by pump 00 and line 4H to furnace l2.Likewise the recycle gas oil can be subjected to solvent extraction andthe rafiinate recycled with fresh feed.

Stabilizer 38 is operated at an elevated pressure in the conventionalmanner. Reflux, pressure, and reboiling are controlled to takestabilized gasoline oil the base of tower 38 through valved line 44 forfurther treatment, storage, or use. Gases eliminated in producingstabilized gasoline pass overhead from stabilizer 38 to condenser 45 byline 46 and thence to reflux drum 1. Condensate is removed from drum 41by means of valved line 48 and pump 49. A portion of it can be returnedto stabilizer 38 as reflux through line 50 and the rest of thecondensate can be withdrawn from the the desired product.

Reverting to stripper 23, the stripped spent catalyst is discharged into"downflow regenerator I! by lines 52 and/or 64. Catalyst can be recycledto reactor l6 by lines 62 and I3 as shown in Figure 2 of the drawing.Make-up catalyst can be introduced to the system as needed, for exampleby line 63. The expression "downflow" as herein employed refers to theflow of catalyst system by valved line 5| as from the regenerator andnot to flow of gases therein.

In my downflow regenerator, air or other oxygen-containing gas can beintroduced at the base of the regeneration zone within chamber I!through line 53. The regenerated catalyst is withdrawn from the bottomof the regeneration zone and the spent catalyst is introduced at a pointabove the gas inlet. Within this regeneration zone a catalyst residencetime suflicient to rmit the combustion of carbonaceous materials isprovided. The catalyst density in theregeneration zone can be.controlled by vapor velocity therein. I employ such gas velocities aswill provide catalyst densities of about to 35 pounds per cubic foot,preferably between about and 30 pounds per cubic foot, for examplepounds per cubic foot. Such gas velocities in this case can rangebetween about 0.05 and 2.0 or more feet per second and are preferablybetween about 0.1 and 1.0 feet per second, all dependent upon catalystsize and particle density. For silicaalumina type catalysts I prefer toavoid temperatures in excess of 1050 F. to 1100 F. but the safe limitwill, of course, depend upon the particular catalyst employed.

I provide for extraneous temperature control by using coils l8 or thelike for circulating a heat exchange fluid such as fused salt mixture,mercury,'molten metal alloys, oil or steam. Likewise the reactor Hi canbe constructed within the regenerator I! as shown in Figure 2.

Regenerated catalyst is withdrawn from the lower portion of theregeneration zone in chamber l1 and is accumulated below theregeneration zone and in standpipe l4. Catalyst is maintained in fluentcondition by means of an inert gas such as steam introduced throughlines 54 and Ma. The amount of aeration gases should be such as tomaintain the catalyst in fluent form and of such density as to providethe necessary pressure head at the base of the standpipe. For obtainingdensities of between about 20 and 30 pounds per cubic foot I employ gasvelocities of between about 0.05 to 0.2 feet per second in the catalyst.

The regeneration gases carry some of the catalyst overhead by line 55 tocyclone separator 56 and the catalyst is returned to the top ofregenerator I! by conduit 51. Additional catalyst can be removed byseparator 59 and returned to regenerator IT by conduit 60. Vent gasesare removed by line 6|.

The flow diagram of my process as well as the description thereof ishighly simplified and various details such as heaters, coolers, pumps,valves, etc., have been omitted which would merely encumber thisspecification unnecessarily. While my invention has been described withreference to certain embodiments thereof, it is to be understood thatthey can be modified in various ways without departing from theinvention and that I do not mean to be limited thereby but only by theappended claims.

I claim:

1. Apparatus for catalytic contacting whereina fluent catalyst isalternately onstream and regenerated comprising a vertical reactionchamber, means for accumulating catalyst from said reaction chamber, avertical regeneration chamber, means for dispersing the accumulatedcatalyst in said regeneration chamber, a substantially vertical conduitof smaller cross-sectional area than said regeneration chambercommunicating with the lower part of said regeneration chamber andadapted for accumulating a bodyof fluent catalyst whereby the pressurehead at the base of said conduit is the sum of the pressure developed bythe weight of the column of fluent catalyst in said conduit plus thepressure imposed at the top of said conduit by superimposed pressure inthe regeneration chamber, means for introducing an inert fluidizingmedium into said substantially vertical conduit at a relatively lowpoint therein a valve below said lastnamed means, a transfer lineleading to the base of said reaction chamber from a point below saidvalve and angularly disposed in respect to said conduit, and meanswhereby catalyst may be dispersed in amounts regulated by said valvefrom said conduit to said transfer line and thence back to the base ofsaid reaction chamber.

2. A catalytic contacting apparatus which comprises a first contactingchamber, a second contacting chamber adapted to effect a net downwardflow of fluent settled dense phase solid catalyst particles therefrom,downwardly extending conduitmeans communicating with the secondcontacting chamber-at a low point therein and adapted to accumulate acolumnar body of settled catalyst particles therefrom, aerating meansfor introducing an inert aerating fluid into said conduit, a valve belowthe aerating means for regulating the flow of catalyst material in theconduit, means for transferring aerated catalyst from a point below thevalve in said conduit to said first contacting chamber, means forsupplying a different contacting fluid to each of said contactingchambers in volume suflicient to maintain a turbulent catalyst phasetherein, means for withdrawing catalyst and contacting fluid from saidfirst contacting chamber, means for separating the catalyst from saidcontacting fluid and means for introducing said catalyst into saidsecond contacting chamber.

3. The method of operating a catalytic conversion system employing apowdered catalyst in conversion and regeneration zones which methodcomprises passing hydrocarbon vapors through a conversion zone incontact with a dense turbulent suspended powdered catalyst phase undersuch conditions as to effect catalytic conversion of said hydrocarbons,removing catalyst from reaction products, stripping deactivated catalystwith an inert gas and introducing said stripped catalyst into aregeneration zone, passing an oxygen-containing gas, upwardly in. saidregeneration zone at such a vertical velocity as to maintain in thelower part of said zone a dense turbulent suspended powdered catalystphase, withdrawing regeneration gases from the top of said regenerationzone, withdrawing regenerated catalyst as a downwardly moving columnfrom a low point in the regeneration zone at which the catalyst densityis at least about-10 pounds per cubic foot, introducing an aeration gasinto the downwardly moving column for maintaining catalyst therein influent condition, suspending said catalyst from the base of said columnat a controlled rate in a hydrocarbon stream and introducing saidcatalyst along with said stream back to said conversion zone.

4. The method of operating a catalytic conversion system employing apowdered catalyst in conversion and regeneration zones which methodcomprises passing hydrocarbon vapors through a conversion zone incontact with a dense, fluid ized turbulent suspended powdered catalystphase under such conditions as to effect catalytic conversionof saidhydrocarbons, removing catalyst from reaction products, strippingdeactivated eans? catalyst with an inert gas and introducing saldstripped catalyst into a regeneration zone, passing an oxygen-containinggas upwardly in said regeneration zone at such a vertical velocity as tomaintain in the lower part of said zone a dense, fluidized, turbulentsuspended powdered catalyst phase, withdrawing regeneration gases fromthe top of said regeneration zone, withdrawing regenerated catalyst as adownwardly moving column from the dense, fluidized catalyst phase in theregeneration zone, introducing an aeration gas into the downwardlymoving column for maintaining catalyst therein in fluent condition,suspending sald catalyst from the base of said column at a controlledrate in a hydrocarbon stream and introducing said catalyst along withsaid stream back to a low point in said conversion zone.

5. The method of contacting small particles of hard solids with threeseparate gaslform streams which method comprises dispersing said solidsin a first gasiform stream, introducing said stream at the lower part ofa first contacting zone l'and passing said stream upwardly in said zoneat a sufliciently low velocity to maintain a dense suspended solidsphase therein, separating solids from said first streamand-countercurrently contacting said separated solids with a secondgasiform stream introducing said countercurrently contacted solids intoa second contacting zone, introducing a third gasiform stream at thelower part of the second contacting zone and passing said third gasiformstream upwardly in said second contacting zone at a sufllciently lowvelocity to maintain a dense phase of suspended solids therein, removingsaid third gasiform stream from the upperpart of said secondcontactingzone while returning entrained solids from said stream to the densesuspended solids phase in the second contacting zone, downwardlywithdrawing solids from the lower part of the second contacting zone asan aerated column of substantial height, introducing an aerating gas ata low point in the column in an amount suiflcient to maintain the columnof solids in fluent form and of such density as to provide a pressurehead at its base suflicient to effect the dispersion of solids from thebase of the column into said first gasiform stream, and utilizing thepressure head at the base of said column for dispersing solids from saidcolumn into said first gasiform stream.

6. The method of effecting catalytic hydrocarbon conversion whichcomprises introducing a hydrocarbon stream into the lower part of areaction zone containing hard, porous catalyst particles of about 400 to150 mesh in particle size, passing said stream in gaseous form upwardlyin said zone at a velocity within the approximate range of .3 to 3 feetper second whereby a. fluidized dense phase of catalyst is maintained insaid zone, maintaining said zone at conversion temperature and pressurewhereby hydrocarbon conversion is effected and carbonaceous materialaccumulates on the catalyst, separating catalyst from said hydrocarbonstream, stripping said separated catalyst with a stripping gas inastripping zone, combining gas from the stripping zone with saidhydrocarbon stream, introducing stripped catalyst from the strippingzone into a regeneration zone, passing an oxygen-containing gas upwardlyin the regeneration zone at a velocity within the range of about .1 toabout 2 feet per second whereby a fluidized dense phase of catalyst ismaintained in said zone, maintaining a temperature, pressure andcatalyst residence time in the regeneration zone for effectingcombustion of carbonaceous materials from the catalyst, separating andreturning catalyst from gases leaving the upper part of the regenerationzone, downwardly withdrawing regenerated catalyst from the lower part ofthe regeneration zone as an aerated catalyst column of substantiallength, introducing an aerating gas at a low point in said column in anamount to maintain the catalyst in fluent form and of such density as toprovide a pressure head at the base of the column sufllcient to eifecttransfer of the catalyst from the base of the column to the lower partof the reaction zone and transferring catalyst from the base of thecolumn to the lower part of the reaction zone by introducing it into thehydrocarbon stream prior to the introduction of said stream into thereaction zone.

7. The method of claim 6 which includes the step of introducing strippedcatalyst into the regeneration zone at an upper level therein.

8. In a continuous cyclic process for the catalytic conversion ofhydrocarbons involving alternately and repeatedly contacting a powderedcatalytic material with a vapor stream of the hydrocarbons in acatalytic conversion zone whereby carbonaceous deposits accumulate onthe catalyst and thereafter contacting the used catalyst with anoxygen-containing gas in a regeneration zone to burn off the deposits,the steps including introducing particles of used catalytic material tothe regeneration zone, flowing a stream of an oxygen-containing gasupwardly through the regeneration zone at a. velocity adapted to form adense turbulent phase of the catalyst particles in said zone, addingused powdered catalyst to said dense phase and withdrawing correspondingamounts of regenerated catalyst therefrom at a rate adapted to maintainthe average resident time of said particles within the regeneration zoneat a suitable value, effecting said withdrawal of regenerated catalystfrom the regeneration zone separate from the gaseous regenerationproducts through a catalyst withdrawal passageway opening directly atthe lower portion of said dense phase, and continually introducingregenerated catalyst thus withdrawn under a pressure head, includingthat exerted by the dense phase of catalyst in the regeneration zoneabove the inlet to the catalyst withdrawal passageway, to said vaporstream of the hydrocarbons passing to the conversion zone.

9. The method of operating a catalytic conversion process employing hardcatalyst particles which method comprises continuously introduc ingcatalyst particles of about 150 to 400 mesh particle size into avertical contacting zone, passing a gasiform stream upwardly throughsaid contacting zone at such vertical velocity within the range of about1 foot to about 2 feet per second as to maintain a bulk catalyst densityin the lower part of said zone of at least about 10 pounds per cubicfoot, continuously withdrawing a gasiform stream from the top of saidcontacting zone, separating catalyst particles from the withdrawn streamand returning the separated catalyst to the contacting zone,continuously removing cata lyst material as a downwardly moving columnthrough the base of the vertical contacting zone from a point in thecontacting zone at which the bulk density of the catalyst is within therange of approximately 10 to 35 pounds per cubic foot, introducing anaerating gas into said column in an amount sufilcient to maintain thecatalyst in fluent form and of such density as to provide a pressurehead at the base of the column sufficient to effect the introduction ofsaid catalyst from the base of said column to a second contacting zone,passing catalyst from the base of said column to said second contactingzone and returning catalyst from said second contacting zone forreintroduction into the first-named vertical contacting zone.

10. The method of converting heavy hydrocarbons into gasoline whichcomprises dispersing small particles of a solid cracking catalystconsisting essentially of silica and at least one metal oxide in agasiform stream consisting essentially of vapors of said heavyhydrocarbons at a cracking temperature, introducing said stream at thelower part of a cracking zone and passing said stream upwardly in saidzone at a sufficiently low velocity to maintain a dense suspendedcatalyst phase therein, separating catalyst from said first stream,stripping said separated catalyst and introducing said stripped catalystinto a regeneration zone, introducing oxygen containing gas at the lowerpart of the regeneration zone and passing said oxygen containing gasupwardly in said regeneration zone at a sufliciently low velocity tomaintain a dense phase of suspended catalyst therein, removing gasesfrom the upper part of said regeneration zone while returning entrainedcatalyst from said gases to the dense suspended catalyst phase in theregeneration zone, downwardly withdrawing catalyst from the lower partof the regeneration zone as an aerated column of substantial height,introducing an aerating gas at a low point in the column in an amountsuflicient to maintain the column of catalyst in fluent form and of suchdensity as to provide a pressure head at its base sufficient to effectthe dispersion of catalyst from the base of said column into thefirst-named stream, and utilizing the pressure head at the base of saidcolumn for dispersing catalyst from said column into said first-namedstream.

11. The method of effecting catalytic cracking of heavy hydrocarbons forthe production of gasoline which method comprises introducing a streamof hydrocarbons consisting essentially of gas oil into the lower part ofa cracking zone containing hard porous particles, about 400 to 150 meshin size, of a cracking catalyst consisting essentially of silica and atleast one metal oxide,

- passing said stream in gaseous form upwardly in the cracking zone at avelocity within the approximate range of .3 to 3 feet per second wherebya fluidized dense phase of catalyst is maintained in said zone,maintaining said cracking zone at a temperature in the range 0! about800 to 1000 F. under a pressure in the range of atmospheric to 50 poundsper square inch gauge whereby catalytic cracking is eflected and acarbonaceous malyst from the lower part of the regeneration zone as anaerated catalyst column of substantial length, introducing an aeratinggas at a low point in said column in an amount to maintain the catalystin fluent form and of such density as to provide a pressure head at thebase of the column sumcient to efiect transfer of the catalyst from thebased the column to the lower part of the cracking zone and transferringcatalyst from the base of the column to the lower part of the crackingzone by introducing it into the hydrocarbon stream prior to theintroduction of said stream into the cracking zone.

12. The method of contacting solids of small particle size with aplurality of gasiform streams which method comprises continuouslyintroducing said solids into a first contacting zone, passing a firstgasiform stream upwardly in said zone at a vertical velocity suillcientto maintain a mass of said solids in dense phase suspension therein,withdrawing said stream from the upper part of said zone, continuouslywithdrawing solids as a downwardly moving column directly from the densephase in said zone, introducing sufllcient aeration gas into said columnto maintain the solids therein in fluent form. dispersing solids fromthe base of said column into a second gasiform terial accumulates on thecatalyst, separating catalyst from said hydrocarbon stream, strippingsaid separated catalyst with a stripping gas in a stripping zone,introducing stripped catalyst from the stripping zone into aregeneration zone, passstream, introducing-said second gasiform streamand the solids dispersed therein at the base of a second contactingzone, passing said second gasiform stream upwardly in said secondcontacting zone at a vertical velocity suflicient to maintain the solidsin a-dense fluid phase therein, removing solids as a suspension in saidsecond gasiform streamfrom said second contacting zone, separatingsolids fromthe withdrawn stream, introducing a third gasiform streaminto the separated solids for displacing at least a part of the secondgasiform stream therefrom, and thereafter returning said solids for saidintroduction to said first contacting zone.

JAMES M. PAGE. Jn.

sameness crran The following references are of record in the nle of thispatent:

UNITED STATES PATENTS Number Name Date 1,475,502 Manning Nov. 27, 19231,577,534 Miller Mar. 23, 1926 1,984,380 Odell n-. Dec. 18, 19342,039,904 Hill May 5, 1'936 2,226,578 Payne Dec. 31, 1940 2,239,801Voorhees Apr. 29, 1941 2,247,097 Menshih June 24, 1941 2,264,438 GaylorDec. 2, 1941 2,270J903 Rudback Jan. 27, 1942 2,273,075 Weems Feb. 17,1942 2,302,209 Goddin Nov. 17, 1942 2,305,569 Degnen Dec. 15, 19422,325,136 Kassel July 27, 1943 2,326,705 Thiele et al. Aug. 10, 19432,327,175 Conn Aug. 17, 1943 2,331,433 Simpson et al. Oct. 12 1,9432,340,878 Holt et al. Feb. 8, 1944 2,300,787 Murphree et al. Oct. 17,1944 FOREIGN PATENTS Number Country Date 23,045 Great Britain 1910331,322 Great Britain July 3, 1940 533,037 Germany Sept. 8, 1931

